This relates to copending Ser. No. 407,428 filed Aug. 12, 1982, now abandoned, and Ser. No. 468,364 filed Feb. 22, 1983, and the same are incorporated herein by reference.
This invention relates to polymeric compositions and processes particularly useful in surface coating compositions, and more particularly pertains to aqueous blends containing certain reactive self-curing water-dispersed polymers, certain water dispersed polyelectrolyte polymers, and preferably containing a polymeric phosphate additive, to provide useful water-based coating compositions for interior beverage and food containers and similar sanitary coating applications.
Water-based coating compositions for use as internal sanitary liners for metal containers are suggested in U.S. Pat. No. 3,991,216. Such polymers are based on interpolymers of copolymerized acrylamide monomer, carboxylic monomer, and other ethylenically unsaturated monomers. However, such polymers are difficult to spray and often exhibit deficient film properties such as lack of resistance to ethanol and hence are undesirable for containers for alcoholic beverages.
It now has been found that certain reactive self-curing water dispersed polymers blended with an aqueous polyeletrolyte and a phosphated polymer provides an excellent sprayable coating suitable for an interior coating for beverage and food containers. The polyelectrolyte polymer is a resinous copolymer polyelectrolyte produced by polymerizing ethylenic addition polymerizable monomers, including carboxyl or hydroxyl monomers, in an aqueous medium containing an ionizing agent. The reactive self-curing water-dispersed polymer contains copolymerized monomers including functional carboxyl, hydroxyl, amine, or amide monomers in combination with alkylol acrylamide monomers. The monomers preferably are polymerized in a step-wise reaction to concentrate the alkylol acrylamide on the surface of the water dispersed polymer particles to provide an improved stabilized water-dispersed polymer exhibiting surprisingly good rheological properties including viscosity, stability and spray application. By concentrating alkylol acrylamide on the polymer surface and by polymerizing at temperatures preferably above 70.degree. C., it is believed that a minor amount of alkylolacrylamide reacts with a minor amount of functional monomer during the addition polymerization of ethylenic monomers to provide a relatively rigid or hard polymer particle surface, which apparently stabilizes the viscosity of the water-dispersed blend as well as provide considerable shear resistance during subsequent spray application of the polymeric blend. Preferred water dispersed polymers are emulsion polymers. Upon ultimately heat curing of the composition of this invention, the self-curing water-dispersed polymer becomes self-curing by the alkylol acrylamide reacting with the functional monomer groups in the polymer. By blending the reactive self-curing water-dispersed polymer with an aqueous polyelectrolyte polymer, the blend provides an excellent sprayable interior coating particularly suitable for beverage cans. A preferred polymeric blend in accordance with this invention contains an aqueous dispersed phosphated polymer. Preferred phosphated polymers are epoxy phosphate polymers. The inclusion of phosphated polymer provides improved coating characteristics such as solvent resistance and improved porosity properties. The polymeric composition of this invention provide improved viscosity, stability, improved mechanical stability, and surprisingly good rheological properties including spray application. Coatings based on the polymeric composition exhibit high molecular weight, high solids, minimal use of solvents, good spray application as well as forming films having good film integrity properties. These and other advantages of this invention will become more apparent by referring to the detailed description of the invention and the illustrative examples.